Lithium Iron battery won't stay charge on the bike

[Tanerrc]

Thanks for the insite JJ. Keep up the good work.

[hannibal]

My understanding of amp hours is that a 14 Ah bettery can produce 14A for an hour, or 28A for 30 mins, or 7A for 2 hours, etc.

Perhaps the ability to produce more current ifor a given period of time is related to charging rates. I've never heard this but it could make sense.

[Grimly]

I have an 8Ah AGM battery in my XS650 (kickstart only), in place of the 14Ah - the charging voltage is absolutely normal.

[jabcb]

Make sure the batteries are fully charged before you do your testing. Otherwise you might just be comparing one fully charged battery to another that's half charged.

[eil]

My questions are:
What am I missing about amp hours here?
Why would different amp hours affect the charging rate?

The capacity of the batteries affects nothing about how the batteries behave except for how long it takes to charge (and discharge them).

The most likely explanation is that the two batteries are at different levels of charge. The battery which has less charge will draw more current, which can pull the voltage down somewhat. A fully charged battery will not draw much current and will show full voltage across the terminals. To check this, charge both batteries fully before putting them on the bike.

Another explanation is that one of the batteries is bad. If you charge them both off the bike and still get the same results, then one of them is probably a goner.

[TxGSrider]

Ive messed with the lithium batteries in my 4 wheelers with mixed results. My biggest gripes were 1) They didn't like to start in really cold weather, and 2) they can't be recharged if the voltage drops below a certain level (and if you try to recharge them or jump them after they run down they'll literally smoke and meltdown). So if you are having a charging problem on the bike that would let it discharge too much, its a good chance it'll be useless... or dangerous.

[Joe Garfield]

My guess is the small battery is on it's way out. 2 times I got bad test results when testing my charging system, due to sh1tty batteries. Both times I replaced the battery with a new one, and both times the charging voltage went up near 14v.

Anyone running a lithium battery needs some special charging circuitry, since 1) they operate at a slightly different voltage, and 2) under/over charging them can cause a serious fire.