How to Test Gel Batteries

A gel-cell battery is different than most traditional batteries in that it is sealed and does not utilize liquid electrolytes. Rather, silica is added to the electrolytes, causing it thicken into a gel that is suspended within the battery. Because of this, gel batteries are spill-proof and more resistant to corrosion. Gel batteries, however, are generally more expensive than traditional batteries and are not able to be refilled. This also means gel batteries cannot be tested with a hydrometer. The simplest and quickest way to test your gel battery is with a digital voltmeter.

Things You'll Need:

• Voltage-limited/float battery charger (if necessary)
• Digital voltmeter
• Box wrench set

1. Access the gel-cell battery by removing the terminal covers

Access the gel-cell battery by removing the terminal covers. Then disconnect the battery from the vehicle. Detach the gel battery’s negative terminal first, followed by its positive terminal. For most vehicles, you will need assorted box wrenches in order to completely disconnect the battery.

2. Attach the voltmeter’s tester leads/clamps to the gel battery

Attach the voltmeter’s tester leads/clamps to the gel battery. The negative tester lead must connect to the battery’s negative post and the positive tester lead to the positive post.

3. Turn on the voltmeter and look at the reading shown

Turn on the voltmeter and look at the reading shown. If your gel battery displays a charge within the 12.85 to 12.95 range, it is 100 percent charged. A voltage of 12.65 means it is only 75 percent charged, while a 12.35 reading correlates to a 50 percent charge.

4. Recharge the gel battery if you receive a low voltage reading

Recharge the gel battery if you receive a low voltage reading. Be sure that you use a voltage-limited battery charger, also known as a float charger, for this task. A traditional charger should not be used on gel batteries, as it may overcharge and damage the battery. A voltage-limited charger will charge at a set rate and turn off when a full charge is achieved.

5. Permit the gel battery to sit for 24 hours after charging

Permit the gel battery to sit for 24 hours after charging. This will allow the surface charge to dissipate and provide a more accurate reading. Retest the gel battery with a voltmeter after the 24-hour period has passed. If your gel-cell battery shows a low charge once again, chances are it will need replaced.

Video: How to test your batteries

Helpful comments on this video:

• Great video. I would rather not be sleeping on top of the batteries but I suppose battery location choices are limited on a boat. I’ve had lead acid batteries last many years and cheaper than lithium even with more frequent replacing. 8 yrs however is excellent and understandably they need replacing.
• We had a set up on Fair Isle where two batteries were mounted some distance from the others and with the positive and negative coming from one end when we bought her. Like you I thought the closer battery would die well before the others as they were working harder. However the distant ones died first I can only assume because of sulfation due to never getting a good strong charge at optimum voltage. (it was a stupidly long wire run, the voltage drop must have been significant even with 00) Lead acid can be a pain, but youre right if your boat is sitting at a dock on trickle charge most of the time as 99% are then theres no point in going lithium. For us cruisers though I think Lithium has just about got to the point that it makes financial sense. Discounting the cash it's a no brainer!