If you’re going on a camping trip or just exploring available options to keep your battery bank fully charged using the grid you’ll probably want to know what charger to use for the bank, recommended charge rate, and the time it takes to fully charge the battery with that charger.
In this post, you’ll find guidance on what charge rate to use for a 400 Ah battery bank, what determines the charge rate, and the time it takes to fully charge the battery.
Note: The information provided below is only intended as a guide. Always consult the battery owner manual or manufacturer for the recommended charging rates.
What Size of Battery Charger for a 400 Ah Battery?
The charge rate (amps) to use for a 400 Ah battery mainly depends on the battery chemistry whether AGM or LiFePO4 and the battery temperature.
Charge rate for a 400 Ah AGM Battery
The recommended rate to use for the battery bank made up of lead-acid AGM battery should be about 40 amps (0.1C).
It will be highest during the bulk charge phase and then gradually reduce after the bulk charge rate has been attained.
Charge rate for a 400 Ah LiFePO4 Battery
A LiFePO4 battery generally can handle higher charge rates compared to an AGM battery. For a 400 Ah LiFePO4 battery, you’ll likely be able to use up to 200 amps (0.5C).
Always confirm if the battery bank can handle this by consulting the charge rate specified in the battery specifications. This is because the recommended charge rate can be lower, for example at 80 amps (0.2C).
Does using a Lower Charge rate (amps) Damage the Batteries?
No, it does not cause damage, it only takes a longer time for the battery to get to 100% of full charge.
In fact, if you’re only using a fraction of its battery capacity, say 10-20%, vs. 50% (AGM) or 80% (LiFePO4), the time to charge will be lower.
Are you only using a fraction of the available battery capacity? If so then you may be able to get by using a charger that has a lower charge rate.
How Long it takes to Fully charge a 400 Ah Battery?
The time it takes to fully charge a battery depends on the charge rate, battery chemistry and how deeply discharged the battery is.
A 400 Ah, 12V LiFEPO4 takes slightly about 2 hours when charged at 200A. This assumes that the battery has been discharged to 80% of its capacity.
Note: This is only a guide – always consult the battery manual for the recommended charge rate to use to charge the batteries safely without affecting their lifespan.
AGM batteries need to be charged at a lower rate and therefore take a longer time to fully charge. At a charge rate of about 40 amps, it can take a minimum of 10 hours and usually longer to charge the battery. This assumes that the battery has been discharged to 50% of its capacity.
If the battery is only partially discharged then it will take less time to fully charge. Undecided whether to invest in AGM or LiFePO4 batteries, my take is if you’re using the batteries on a daily basis and you need them recharged in a short period of time then go for LiFePO4 battery time.
They are smaller, weigh less, and last longer though cost considerably more than the AGM battery. If budget is an issue and can go live with the longer charge times then go for the AGM battery.
Closing Thoughts
As a general rule always consult the battery manual for the recommended charge rate for your battery type. With that said,
A 400 Ah LiFePO4 battery can usually be charged at up to 200 amps (check with your battery type), with an estimated charge time of about 2 hours.
This assumes that the batteries have been deeply discharged to 80% of their capacity.
AGM lead acid 400 Ah battery bank on the other hand should be charged at the lower 40 amps (0.1C).
Expect a minimum charging time of at least 10 hours if the battery has been deeply discharged to up to 50% of its capacity.
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