Automotive Battery Voltage Indicator for Lithium & Lead-Acid Batteries – Guide

Last updated on November 5th, 2018

Nothing sucks more than turning your ignition key…only for nothing to happen. Well, almost nothing. It goes head-to-head with having to repair a flat tire on the go. The best way to avoid a dead battery is to check its voltage every once in a while. There are a few ways to make that job a bit easier. One interesting option I’ve found recently is the JS-8T Battery Voltage Indicator. What makes it pretty unique is that it’s compatible with any battery chemistry, including Lithium and Lead-Acid. That makes it perfect for cars, motorcycles and RC devices alike. Plus, it sure beats having to dust-off your jumper cables.

Note – Nothing in this post is sponsored or was received for free. This is just just my own personal opinion based on my experiences.

Why you should have a battery indicator

Having to jump-start your car when you're late to work is no fun. While portable jump starters have made the job a lot easier, it's best to keep an eye on voltages.
Having to jump-start your car when you’re late to work is no fun. While portable jump starters have made the job a lot easier, it’s best to keep an eye on voltages.

Sure, for the mechanically minded, a run-down battery is little more than a five-minute inconvenience. We’re the type of folks our friends always resort to for jumper cables. And now, with battery packs like the 600 Amp Lithium Jump Starter in my Genesis Coupe above, we don’t even need another vehicle. But the problem isn’t just starting the engine – it’s the wear and tear that low-voltage causes to car batteries.

The number one cause of prematurely dead batteries is over-discharge. If you never let your battery go below 11v, you can reliably expect it to last 5 years or more. However, if you take the same battery, drain it under 10v and leave like that for just a few days…it’ll rarely last more than a year. It’s simply the nature of battery chemistries. And contrary to popular belief, Lithium batteries are no less susceptible to over-discharge. What’s more, over-discharging below 10v will void most automotive battery warranties. If you don’t believe me, check it for yourself.

In other words, keeping your battery charged will pay for itself over the years. One way to do that is  keeping the battery permanently tethered to a smart battery charger. But that can be a PITA. The next best thing is simply to be diligent checking the battery voltage. Just like you do with tire air pressure…I hope.

The option I went with

The main issue with most battery checkers is that they’re bulky, awkward to install and not versatile. Especially for motorcycles where both battery drain, size or aesthetics are a big concern. Plus, most are made for lead-acid batteries and wholly unsuitable for Lithium batteries. Looking for a good battery voltage indicator for my Ninja 650, I stumbled on this unit, the JS-8T Battery Tester. The cool thing about it is that it’s cheap, compact and discrete.

The power button allows me to turn it off so it isn’t distracting or wasting battery when not needed. That way I can connect it directly to the battery instead of an auxiliary circuit. And the programmable feature means I can adjust it to my battery type, so that it won’t be useless if I install a light-weight lithium battery.

As far as the cons go, the only big one is that it isn’t really waterproof. While it should be able to take a splash without issues, for anything else I wouldn’t trust it as-is. Thankfully, it only took a minute to pop off the back cover and apply some conformal coating to it. The coating is simply a waterproof, non-conductive silicone “paint” to protect circuit boards. With that I’d say it qualifies as water-resistant.

But what really makes the JS-8T stand out is that it’s programmable. That’s what we’ll be talking about next.

JS-8T Battery Voltage Indicator Specifications

  • Model: JS-8T
  • Size: 31*7 mm / 1.22*0.27 in Approx.
  • Input voltage: 8-65V
  • Panel Mount Hole: 28.5mm
  • Panel Mount Thickness: 2mm
  • Quiescent Sleep Current: 10uA
  • Voltage Steps: 8 Bars
  • Electric Current: 5mA
  • Backlight Color: Red, White, Green, Blue
  • Weight: 6 grams
  • Protection: Revered Polarity Protection

Setting up the JS-8T Battery Tester

This chart will tell you what voltage corresponds to each level for your battery. To program your JS-8T for a different battery, you'll need the voltages in Green under 'LED1' and 'LED2'. Note - Feel free to use other voltages.
This chart will tell you what voltage corresponds to each level for your battery. To program your JS-8T for a different battery, you’ll need the voltages in Green under ‘LED1’ and ‘LED2’. Note – Feel free to use other voltages.

The programmable part might seem a bit unnecessary if you’re unfamiliar with batteries. How a battery voltage indicator works is by correlating the battery’s voltage with its capacity. It assumes that, say, 10.5v is a dead battery and 13v fully charged. The problem is that there’s a lot of different types of battery chemistries with different voltage curves.

If you’re reading this, then DIYing is probably a hobby of sorts for you. And as such you probably have more than one set of wheels lying around. Not to mention a fair share of batteries or all different types. The cool thing about this battery monitor is that you can program it for Lead-Acid car batteries, AGM, Lithium motorcycle racing batteries, or anything else. You can even use it for Drone or RC battery packs, regardless of it being 4 volts or 48 volts.

The point of programming is making sure that the voltage monitor accurately gauges the state of charge of your battery. Lithium batteries have a notoriously more “flat” curve than lead-acid. That means it will stay close to 12v for the vast amount of its charge, and then drop right into over-discharge. Lead-Acid on the other hand has a softer curve, giving you a better understanding of its state of charge from its voltage. Lithium batteries are becoming pretty affordable, and are typical in the motorcycle world. And if you’re into RC drones, battery packs are tossed around like candy. Having one solution that works for everything is infinitely easier.

In most cases, your JS-8T will probably come preconfigured for standard 12v batteries – unless specified otherwise. You can always just test it in practice first. You only have to bother programming it if you find it isn’t accurate for your particular battery or you want more precision.

Note – Feel free to use different voltages

The voltage chart above is just a suggestion. The best thing you can do is ask the manufacturer of your battery at what voltage you should recharge the battery, and at what voltage it is fully charged.

In the case of the Antigravity Lithium Battery I installed in my motorcycle, the manufacturer recommends never letting the voltage go below 11v, and to not charge over 13.2v. In my case, those would be the ‘LED1’ and ‘LED2’ voltages I’d use, respectively.

What you’ll need to program it

Your unit might be perfectly programmed for your battery out of the box. But if not, all you need to program the JS-8T is an adjustable voltage source of any kind. Like this tattoo power supply.
Your unit might be perfectly programmed for your battery out of the box. But if not, all you need to program the JS-8T is an adjustable voltage source of any kind. Like this tattoo power supply.

Regrettably, programming the JS-8T isn’t as easy as flicking a switch. The good side of that is that you can program it exactly how you want. The bad side is that you’ll need an adjustable power source.

  • Adjustable Power Supply – Just make sure it’s adjustable and goes up to the maximum voltage of your battery. The current output doesn’t matter. For a cheap, portable voltage, I like using something like the tattoo power supply shown above. If you go this route you’ll probably also need a plug switch. A Digital Lab Power Supply would be even better, but hardly necessary for a job like this.
  • Power Leads – You’ll need a cable to hook up the power supply to the battery voltage monitor. If you’re a cheapskate like me and are using a tattoo power supply, you’ll probably want to fabricobble your own. All you need to do is add some alligator clips.
  • Multimeter – Optional – If you want to be extra precise, you can double-check the voltage coming out of your power supply with a true multimeter.

If you don’t have and don’t want an adjustable power supply, then things get a bit more complicated. But you could definitely make do with a full battery and a handful of resistors via a voltage divider. But personally I’d advocate for just getting an adjustable power source. They’re cheap and super useful even for occasional DIYing.

JS-8T Programming Instructions

  1. Disconnect the JS-8T Battery Voltage Indicator from your battery.
  2. Turn on your adjustable power supply and set it to the voltage of your battery. Then turn off the power supply. Normally there will be a switch at the back or a button somewhere.
  3. Hook up the JS-8T to your power supply leads. Be mindful of keeping the right polarity.
  4. Press and hold the Power Button on the JS-8T Battery Voltage Indicator and, while it is still pressed, turn on the power supply. After a second or two the first red LED will light up, indicating it is in ‘Programming Mode’. The second LED might stay lit. The goal is connecting it to voltage while the button is pressed.
  5. Set the power supply to the ‘LED 1’ voltage in the chart for your battery type. In this case, for a 12v Lead-Acid battery, that’s 10.5V. If you want to set it a little higher or lower, feel free to do so. If you are using another battery type, choose that instead. This is the voltage that will represent your battery being fully drained.
  6. Press the main button once the voltage is stable at ‘LED 1’ voltage to save that value.
  7. The 7th and 8th LEDs will start flashing, indicating its expecting you to set the upper voltage limit. Adjust your power supply to the ‘LED 8’ voltage and once it is stable, press the center button on the JS-8T.
  8. And you’re done! Programming is complete. Test the battery monitor adjusting the voltage on the power supply between ‘LED1’ and ‘LED8’ voltages. You’ll see how the graph instantly rises or falls to indicate battery charge state.
Note – Don’t use a battery tester to check your charging system

While a healthy 12v battery’s voltage is typically in the 10.5-13v range; charging voltages of 14v or over are typical. And by charging I mean any time the engine is running and the alternator supplying current to the battery. Be it a car, motorcycle or a lawn mower.

As such, this tester can’t really be used to determine if the alternator is working well or not – as would be the case with any such battery indicator. The only exception would be if the charging system is completely FUBAR. Or in other words, if the battery voltage is lower than some 13v (for a 12v battery), and does not increase when the engine is turned on.

This only applies to vehicles with an alternator or charging systems – RC vehicles and drones need not apply.

JS-8T Mounting & Installation

Given how compact it is, you can install it pretty much anywhere - including panel -mounting it.
Given how compact it is, you can install it pretty much anywhere – including panel -mounting it.

Installation couldn’t really be more straight-forward. You can simply use Heavy-Duty Double Side tape to adhere it anywhere. Or for a more permanent installation, you can drill a 25.8mm hole in your dash (cigarette lighter size), and panel-mount it. It simply clips in place.

As far as wiring goes, connect the red wire to battery’s positive terminal, and the black wire to the battery’s negative terminal. You can also hook it up to any wire with a good connection to the battery, such as a cigarette lighter outlet. Just make sure to use proper practices, and remember that it’s almost always preferable to crimp rather than solder on vehicles.

Other Options

There are plenty of other battery monitor options. Where I have space, I like this Noco GC016. However, due to its size and format it isn't suitable for every application.
There are plenty of other battery monitor options. Where I have space, I like this Noco GC016. However, due to its size and format it isn’t suitable for every application.

What battery voltage monitor is right for you will depend on your vehicle and preferences. Especially when it comes to space considerations or battery chemistry. Personally, if I have the space to install it, I like the Noco GC016 on my Ninja 300 seen above – mainly because I can charge it through the same port. On smaller motorcycles, you can ever use the port for jump-starting! The only problem is that it does not play well with Lithium Batteries.

On the other hand, if you have an empty cigarette lighter port, a great option is the one used in my USB Charger/Voltmeter Install for the Ninja 650. Plus, it doubles as a phone charger. If you have a blank panel or empty space on the dash, it certainly is worth considering. However since you can’t turn it off, it has to be connected to an auxiliary circuit. The downside of that is not being able to check the voltage without the key.

On bigger vehicles like RVs, boats or solar panels, other more complex systems are probably more appropriate. In particular, any system with multiple banks of batteries. It all depends on your situation and how much you’ve invested in your batteries.

What about wireless Bluetooth battery voltage monitors?

While Bluetooth Battery Monitors sound like a great idea, in practice, they don't really provide any benefit. It just means another app to have on your phone taking up space and draining battery.
While Bluetooth Battery Monitors sound like a great idea, in practice, they don’t really provide any benefit. It just means another app to have on your phone taking up space and draining battery.

You might stumble upon Bluetooth Battery Voltage Checkers. I’ve tried them, and I’ve ditched them. They used to be great, but as of this review, Android broke the usefulness of the device. I can’t speak for iOS, however – I’ve never owned an iPhone. The problem is they won’t automatically notify you when your battery starts to get low.

Before, without having to open the app, you’d get a notification if the battery was low as soon as you passed by the vehicle. Now, you have to either run the app permanently in the background, or open it up manually to check the voltage. That kinda defeats the purpose of not having to think about it yourself. It takes me way less time to take a glance at this physical battery voltage indicator than to wait for the app to load and check it.

The only real usefulness is if your battery is truly inaccessible and there’s no good place to install a physical battery voltage indicator. The day the wireless battery voltage checkers can push notifications to your phone again, then they’ll definitely be worth taking a look at. Until then, I’d personally avoid them.

But wait…the battery voltage is good, but the engine won’t start

A multimeter is near-useless to determine a car battery's state of health. For that you'll need either the tried-and-true Carbon-Pile Load Tester, or the newer style of Digital Battery Analyzers (like the one pictured here).
A multimeter is near-useless to determine a car battery’s state of health. For that you’ll need either the tried-and-true Carbon-Pile Load Tester, or the newer style of Digital Battery Analyzers (like the one pictured here).

One situation you might encounter is the battery voltage being 12v, but the engine still refusing to start. As surprising as that might sound, it’s the trademark symptom of a sulfated/dead battery. An issue that plagues cars and motorcycles alike.

You can’t gauge the condition of a high-current battery with only a multimeter. To accurately determine the health of a battery, you need a specialized battery tester. The reason is because these types of batteries need testing under stress. That is, you have to measure the battery voltage while you’re putting a drain on it.

Battery testing options

Testing an automotive battery yourself to see if it’s good or bad is pretty easy. There are two main ways to do so, but both are easy and they both work just as well.

With the classic Carbon-Pile Load tester, you hook it up to your battery and rotate the knob or push a switch to apply a load. If the voltage drops below around 11v, your battery is dead or dying. Pretty straight forward and it takes mere seconds.

With the new crop of Digital Battery Analyzers, it’s even easier. These measure battery health by proxy, measuring its internal resistance. It’ll tell you the Cold Cranking Amps to the exact percent at the push of a button. Plus it’s a lot more compact than the traditional option.

Given how common-place dead batteries are, a true battery tester definitely has its spot in any garage. Either will save from wasting time trying to charge a dead battery. Or from getting tricked into replacing a perfectly good battery by the pimpled-teen at the autoparts store.

Conclusion

Moral of the story? For the good of your vehicle (and your wallet), keep an eye on battery voltage. How you do it is up to you.
Moral of the story? For the good of your vehicle (and your wallet), keep an eye on battery voltage. How you do it is up to you.

All in all, there are plenty of options to make sure you’re never caught off guard by a dead motorcycle or car battery. I’m sure that over time we’ll have even better options. But as far as I’ve seen, the Programmable JS-8T Battery Voltage Indicator is my current favorite.

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