It is generally not recommended to parallel lead acid batteries with lithium batteries. However, if one must do so, a battery management system can help manage voltage and charge levels effectively.
Can a lead acid battery be connected in parallel?
In theory it is OK to connect them in parallel with two conditions: Each battery must be in a state where it can be voltage charged. This is fine for lead acid batteries unless they are very run down. Very discharged lead-acid batteries have to be charged with fixed current until they get to a minimum voltage, then they can be voltage charged.
Can You charge lead acid batteries together?
Charge them separately with a good (3 or more stage) battery charger and see if they hold their charge for a day (setlling at about 12.6 or 12.7 V), or if they charge at all. If they do, you can probably safely charge them together. There are always risks involved when charging lead acid batteries. Keep them well ventilated and fused.
Can You charge a lead-acid battery in parallel?
Most lead-acid batteries charge at a constant 14 4 volts, so charging several in parallel is really just a charge-current issue. If the charger cannot supply enough current it will likely lower the charge voltage to protect itself.
What voltage should a lead acid battery be charged at?
Lead acid batteries will not be properly charged at just 13.8 V. All (not some) lead acid batteries I know need a “bulk” charge voltage over 14 Volts (look up the datasheet of any lead acid battery to confirm this). 13.8 V is just to maintain the charge (“float voltage”).
Very discharged lead-acid batteries have to be charged with fixed current until they get to a minimum voltage, then they can be voltage charged. The power supply is capable of maintaining the fixed float voltage. In practise, I think it's a good idea to put at least a diode in series with each battery just because stuff happens.
Do you need a fuse for a lead acid battery?
In actual practice, people put lead acid batteries in parallel and cycle them that way frequently. Just look at RV's and boats and off-grid installations. A fuse for each battery would not be a bad idea. If you are charging them all anyway then what does it matter if one discharges into another?