replace one or both house batteries?

[aztec7fan]

recently had some problems with my house batteries discharging too quiclky.  i took both to my local parts store and one tested fine, but the other tested bad.  should i replace both or just the bad one?  they both are not too old, with a sticker from 2019.

if it matters, this is a 2003 Dolphin on the Workhorse chassis.

thanks,

chris g.

[rossboyer]

It looks like you have two 12 volt batteries in parallel, but even if they were 6 volt in series, I would replace both. A old battery will probably cause problems with the new one as time goes on. If it were me, I would use two 6 volt AGM wired in series to get more capacity if your battery compartment will allow additional height. 

[sstgermain]

Both… Never just one

[rayin]

An older battery will drag down the new battery, both are charged at the same rate but the new battery is over-charged because the old battery will not accept the same amount of charging. The old battery is still trying to reach full charge while the new one is being over-charged.

Now if the older batter is less than 6 months old and passes a full-load test, it may be retained with a new battery.

As to battery type, you have room for 2 batteries; if you were to install 2 6V batteries and one goes bad you are SOL, but with 2 12V batteries you still have one to supply voltage to your coach by simply disconnecting the bad battery. This means you may disconnect your bad battery now and still use your MH.

 

[five]

Get two new 12v...as noted, the bad one will drag the good one down.