12v battery maintenance.

The battery indicator does not measure the electrolyte level, but rather, the specific gravity. As such, the indicator measures charge. It is quite possibe that if you had simply charged the battery, the cranking amps would have returned to normal (or, perhaps the battery is actually failing but not because of low electrolyte). I think some have had premature battery failure because low usage can cause the battery to discharge and repeated low charge levels will significantly degrade a battery. Have you been driving freqently, of have you had significant periods where the car has been idle?

I do agree that the electrolyte should not become especially low with a 'maintenance free' battery... Normally adding water is not necessary. When you looked in and found the 'low' level, were the plates still submerged, or could you see that the top of the plates were dry? Unless the top of the plates become dry, adding water may not accomplish anything.

 

You're right of course !
I hadn't looked carefully at the "eye", and it does indeed indicate both low charge and low electrolyte level. It is a little tricky to interpret because of viewing angle and lighting. I just looked at mine (3Y, ~30K miles) and I beleive it indicates both good charge and good water level.

Based on your experience however, it might be good for people to check on this. One cause of low electrolyte is overcharging. The vehicle manages this (unless someone regularly uses an external charger). Perhaps the Clarity is being a little too aggressive when charging the 12V battery and is causing low levels over time.

To actually access the water level, do the 6 small plastic "Phillips Head - looking" screws across the top un-screw? I tried a couple of mine and they weren't loosening before they began to distort, so I stopped trying.

Yes, The warning lights after a 12V power loss has been repeatedly noted as "normal" for the Clarity.
Like you, this puzzles me... It is very odd that the vehicle would assume that all these problems exist just because power was interrupted. Your experience of driving a few miles to clear them is exactly right, but Honda could have done a better job on this one.

 

That’s quite a bit of water to add to such a small battery. To what level did you fill the cells? Up to the bottom of the fill opening? A half an inch below the opening? Just above the plates by a 1/4-1/2”?

Requiring that amount of water, in my experience, would indicate that either the battery was not properly filled prior to being placed in service or, it has been subject to repeated deep discharges and numerous equalization cycles. Typically, a couple of deep discharges will kill the battery and an equalization isn’t possible under normal operating conditions.

 

Battery replaced proactively. Vehicle purchased Dec 2017, 48k miles. With vehicle off in 50 deg garage, voltage measured 12.4, dropping to 12.2 with lights on.

Not sure why nothing on the original battery told me the size to buy. Thanks to the forum for identification of 51R, bought at Wallyworld for $140.

Further detail:
- Electrolyte level was right in the middle between Lower and Upper Level lines on the original battery. Eye reported good.
- Original battery says 310 CCA and had a 3yr warranty from Honda, but could find no replacement with CCA that low with 3yr warranty. Japan must make the best batteries.

 

FWIW: The Honda replacement battery carries a 100 month warranty, prorated after 36 months. I believe it is priced similarly to what you paid at Walmart. Costco caries an Interstate 51R for $100, which has a 36 month warranty.