OK, so you are sharing your 42x5= 210Ah of discharge (note, Ah = amp-hours, not A = amps, for capacity) between 5 batteries, so 42Ah each. Or 42% depth of discharge over 5 hours, equating to complete discharge over 12 hours. This is faster than the 20-hour rate lead acids are usually rated for (except tractions, for which the capacity is usually given at 5-hour rate) so their effective capacity will be less than 100Ah. But not catastrophically so, perhaps we could say it's a 50-60% depth of discharge each day which a leisure battery will stand. So the discharge side of things is reasonable.
Charging - there is no way to 'fast-charge' a lead-acid, as there is for a Li-ion or a NiMh. The chemistry limits the maximum rate of charge as full-charge is approached, otherwise it will gas heavily and be damaged. With an intelligent 3-stage charger, that goes through bulk, equalise and float stages, you can recharge a flat lead-acid to 100% in 12-16 hours, if it is correctly sized, and yours won't be flat, so this is also do-able. Of course, near the end the charge rate will be low, so the initial charge rate will need to be more than 42Ah*efficiency/available charge time. A suitable charger for the whole bank might be 30-40A output, as this will be able to supply much of the needed charge in the first half of the cycle, ready for the rate to fall off.
40A regulated intelligent chargers are expensive, so you might choose to split the battery bank into individual batteries for charging and if possible, use them independently as suggested above, which can avoid the problems mentioned if they are in different states of charge for whatever reason. Five 8A chargers won't break the bank and will work in either case.
If you must parallel them, then ensure any switching is very low resistance to avoid differing rates of discharge, and fusing as mentioned above. Charger outputs are usually floating so you only need to break one pole of the circuit between the batts. The maximum currents are not very high (you're not running starter motors etc). However, if you parallel up two batteries of very different states of charge, there will be circulating currents and the load won't be shared equally, so the relays should all be fully rated for the maximum currents involved or perhaps 100A, not just a fraction of the load.
FWIW on my boat the six 120Ah batteries are paralleled for charging (alternator, or 30A charger) but discharged in groups so that domestic loads can't flatten the navigation services or engine starter batts, and the inverter doesn't make the lights dip! This is done with relays and I haven't touched the system since I put it in about 20 years ago. I average about 8 years use from a set of batts but they are not often run below 20%-30% depth of discharge.
Charging - there is no way to 'fast-charge' a lead-acid, as there is for a Li-ion or a NiMh. The chemistry limits the maximum rate of charge as full-charge is approached, otherwise it will gas heavily and be damaged. With an intelligent 3-stage charger, that goes through bulk, equalise and float stages, you can recharge a flat lead-acid to 100% in 12-16 hours, if it is correctly sized, and yours won't be flat, so this is also do-able. Of course, near the end the charge rate will be low, so the initial charge rate will need to be more than 42Ah*efficiency/available charge time. A suitable charger for the whole bank might be 30-40A output, as this will be able to supply much of the needed charge in the first half of the cycle, ready for the rate to fall off.
40A regulated intelligent chargers are expensive, so you might choose to split the battery bank into individual batteries for charging and if possible, use them independently as suggested above, which can avoid the problems mentioned if they are in different states of charge for whatever reason. Five 8A chargers won't break the bank and will work in either case.
If you must parallel them, then ensure any switching is very low resistance to avoid differing rates of discharge, and fusing as mentioned above. Charger outputs are usually floating so you only need to break one pole of the circuit between the batts. The maximum currents are not very high (you're not running starter motors etc). However, if you parallel up two batteries of very different states of charge, there will be circulating currents and the load won't be shared equally, so the relays should all be fully rated for the maximum currents involved or perhaps 100A, not just a fraction of the load.
FWIW on my boat the six 120Ah batteries are paralleled for charging (alternator, or 30A charger) but discharged in groups so that domestic loads can't flatten the navigation services or engine starter batts, and the inverter doesn't make the lights dip! This is done with relays and I haven't touched the system since I put it in about 20 years ago. I average about 8 years use from a set of batts but they are not often run below 20%-30% depth of discharge.
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