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There is a common misperception that charging one's battery banks faster is better or worth throwing more money at. Here are some reasons it is not always true:
Lead batteries have a maximum amount of current they will accept, typically C/3 for AGM and C/5 for flooded. So if you have 100Ah of AGM the most it will want to take is something like ~33A. Once the battery's limit is hit throwing more charging capacity at it can't charge it any faster.1)
Deep-cycled lead batteries have a lengthy Absorption stage that cannot be sped up. Depending on use, Absorption typically requires several hours.There is a saying that “it takes 9 months to make a baby, but two women cannot make a baby in 4.5 months”. Same with absorption - it takes what it takes and you cannot hurry it in the normal sense.
However:
charge current affects the SOC transition point from bulk to absorption charging - MaineSail2)
MaineSail found that
Note that the using 2x the charging current only sped up the whole process by 12 minutes (3.6%) due to Vabs starting earlier but taking longer. Getting to Vabs faster could be preferable on PWM controllers.
Also note that for simple, timer-based Absorption configurations4) the slower charging regiment would actually complete more Absorption.5)
Lithium batteries can slurp up current wildly, but shouldn't for their own health. Lithium lasts longest in sub-C use (ie, less than 100A for a 100Ah Li bank). C/2 (50A) is a more common limit to keep from stressing them. In commercial examples the BMS will limit current to protect the cells. A small DC-DC charger can help protect bare cells from their own greediness.