Monday, December 4, 2023


Are “maintenance-free” batteries really maintenance free?

gary-736Dear Gary,
How do I know if I have maintenance-free batteries in my motorhome or if I have to periodically check the water levels? —Kirk P.

Dear Kirk,
I’m guessing you’re referring to the automotive start battery in your motorhome. Those so-called maintenance-free batteries will have non-removable cell caps or no caps at all. Personally, I believe the moniker “maintenance free” is really a misnomer in that even if a battery has no access to measure the specific gravity of each cell using a hydrometer, still the battery and its terminals must be kept clean and free from oxidation and corrosion. In other words, there is still maintenance to be performed if you want to get optimum performance out of those batteries. 

Rather than specific gravity readings, voltage measurements can suffice for checking the state of charge of batteries without access to each cell (I’ve included a chart below):

Open Circuit Voltage vs. State-of-Charge for 12-volt Batteries of Various Types

                                        Battery Electrolyte Type
State of Charge       Flooded            AGM             Gel
100%                           12.6                 12.9             12.8
75%                             12.4                 12.7             12.6
50%                             12.2                 12.4             12.3
25%                             12.0                 12.0             12.0
0%                               11.8                 11.8             11.8

But if you do not see removable caps on the top of the batteries, chances are they are probably considered the maintenance-free type. Keep in mind, some batteries by certain makers may have only two caps that cover three cells each; they may not have six individual cell caps. Hope this helps!

Read more from Gary Bunzer at the See Gary’s videos about RV repair and maintenance.





0 0 votes
Article Rating
Subscribe to comments
Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Oldest Most Voted
Inline Feedbacks
View all comments

Rob (@guest_27384)
5 years ago

Hey Gary,

Thinking of going Lithium battery (s) for my 5th wheel. Could you advise your thoughts on Lithium?



Ronald Payne (@guest_27007)
5 years ago

Hey Gary,so buying a battery with removable caps is better?
Personally,would rather be able to check levels as to so called maintenance free,

Sign up for the

RVtravel Newsletter

Sign up and receive 3 FREE RV Checklists: Set-Up, Take-Down and Packing List.