Decided I need a battery charger onboard. Have 3 27 series batteries now. Is a 20 amp charger sufficent for this setup or should I go for the 30 amp. Any downside of going with the 30,such as overheating batteries and warping plates?
Guest, as an example has 15, 30 and 45 amp chargers that can handle three batteries.
Nothing wrong with 30 amp for three batteries.
The better chargers have three charging stages that drop the voltage load as the current draw drops on the charger when the batteries near full charge. Guest chargers then usually trickle charge at 10% load to maintain batteries.
The 15 amp charger would be too slow. Most double battery setups go for 20 amp chargers.