Hi all. If it takes a 52ah battery 10 hours to charge how long will it take a 35ah battery to charge?
10 hours.
Yes I know it seems daft but time is the main factor not charge rate. So with any lead acid battery as it discharges the sulphuric acid is turned into water and sulphur, and the sulphur is deposited on the battery plates, the longer the sulphur stays on the plates the harder it gets, so if you discharge a battery 20% and start the recharge one minute latter, then in one hour the battery is likely charged, but if you wait 8 hours then start to recharge then likely 10 hours, wait a month and likely will take a week to recharge.
It is not how fast the charger is, but how fast the battery will accept the charge. OK there are ways to recharge batteries faster, with a flooded lead acid (that means you can top up the electrolyte with distilled water) you can use a stage charger or a pulse charger to recharge the battery fast, but with a sealed battery valve regulated lead acid (VRLA) or absorbed glass mat (AGM) the charge rate needs to be carefully controlled.
With a 90 Ah battery using a smart charger rated 3.8 amp likely it will only charge at 3.8 amp for ½ hour, after which it will charge at a lower rate, and with a 35 Ah battery using a smart charger rated 3.8 amp likely it will only charge at 3.8 amp for ¼ hour, after which it will charge at a lower rate, so the difference in charge time is ¼ hour between the two batteries.
This
is typical of the charge pattern from a battery charged with a smart charger, you will note a very short time being charged at 3.8 amp = approx 58 watts, the meter measures watts the charger is using, then slightly longer at 3 amp = 52 watts, with the charge rate at 0.8 amp = 12 watts not being completed, it would have in fullness of time dropped to 0.1 amp and finally off.
Because most of the time the charge rate is very low, time to charge is rather long, this is why lead acid is not suitable for most electric vehicles, it was OK for fork lifts, milk floats, mobility scooters all always recharged at their base and used for less than 8 hours a day. But for cars, push bikes, etc, what the battery both light as possible, and ability to fast charge.
The AGM or VRLA can charge faster than flooded, but to do so the vehicle has to map the battery and hold the battery at 90% charge for a week but then allow full charge once a week to prevent battery damage, so it can only be done with computer control and with a vehicle in regular use. My wife's car with stop start with the lock down has required the battery to be recharged with a smart charger as used so little.