Sizing a Battery Charger

Question:

I have a 2 battery setup as it came from the factory. 1 engine battery and 1 house battery both are 85ah 12volt sealed lead acid. The boat came with a 40 amp ProNautic charger, would you say that this is too big and advise I fit a smaller charger?  - Richard

Answer:

Hi Richard, when sizing a battery charger, you should have at least 10% of battery capacity as a charge rate. Your current battery capacity is 170 amp-hours, i.e 10% of 170 is 17 amps. Your 40 amp charger is definitely bigger than the minimum requirement, but it’s no reason to change it. I recommend you keep that charger, it’s a good size and quality.  -Jeff