Dual battery of different types

[dan4jeepin]

I moved up from a popup to a bigger trailer this year and took my less than a year old high end AGM deep cycle battery off the popup before I sold it. The new trailer came with a new AC/delco Marine battery which isn't as high of quality so I put my deep cycle battery on instead and have the new battery is just sitting around.

Question is would running both battery be a good idea? Would I get longer run time when boone docking or would it just hurt the nicer battery.

[Loefflerh]

No technical answer but thats what I did: wired a Walmart deep cycle marine battery parallel to the existing factory one - different brand, about same size. Result double the capacity (run time) and after 3 years still going strong...

[Herk7769]

Not an easy answer, but yes it will work if properly wired; and no, it is not optimum due to uneven charge and discharge rates.

This happens due to different manufacturers using different internal geometries to get the most amp hours out of the same footprint battery.

Make sure you wire to minimize the external battery resistance as you will only make a non-optimum situation worse. One battery will "loaf" while the other takes most of the load and the more powerful battery will stop the recharge process early so your working battery will not be fully recharged.

Note that the wires that parallel the batteries should be as large as possible and of as equal in length as possible so that the charge and discharge drop is as equal as possible between the batteries.