Hi Tumblehome2 and welcome to the forum.
A few questions, comments and suggestions.
If you combine the two old batteries into one bank will that be for starting the engine
or as a second house bank?
If as a second house bank what will you use to start the engine?
If one of the old batteries is dying it is not a good idea to keep it, especially connecting it to another, good battery.
To give good suggestions on how to deal with your situation it would help a LOT if you could give more details:
- How big and what kind are the existing batteries?
- How much power are you drawing from your house bank?
- Really need to know the output of the solar charger
. If you have a big load and low rate of charge you will just kill any new batteries you buy.
- Why only charge the start battery from the alternator
? The start battery only uses a very small amount of power when starting the engine. All charging
should really go to the house batteries which typically use a lot of power every day running lights, pumps and such.