RV Battery Water Loss: Why Some Batteries Boil More Than Others

The Quick Answer

Your two Interstate golf cart batteries are being overcharged due to an imbalanced charging system or a faulty converter/charger in your 2015 Tiffin Allegro Open Road. The constant bubbling in three cells of each battery and excessive water loss are classic signs of overcharging, even though the batteries test as "good." Since you keep the motorhome plugged in continuously, your charging system is likely delivering too much voltage to those specific batteries in your four-battery bank. You should replace those two batteries now and investigate your charging system to prevent this from happening to the replacements.

What's Causing This

The constant bubbling you're seeing is electrolysis - your batteries are literally being cooked by excessive voltage. In a four 6-volt battery setup like yours, the batteries are wired in series-parallel, creating two 12-volt pairs. When one pair receives higher voltage than the other, those batteries will overcharge while connected to shore power continuously.

Several factors could cause this imbalance in your 2015 Allegro Open Road. Your converter/charger may be developing voltage regulation problems after 9 years of use. The battery cables connecting the problem batteries might have higher resistance due to corrosion or loose connections, causing the charging system to compensate with higher voltage. Additionally, the battery temperature sensor (if equipped) might be malfunctioning, preventing the charger from reducing voltage as batteries warm up.

The fact that only three cells in each problem battery are bubbling while the fourth isn't suggests internal damage has already begun. These batteries have likely suffered permanent capacity loss and sulfation damage from the prolonged overcharging, even though they still "test good" on a basic load test.

Tools You'll Need

• Digital multimeter capable of DC voltage measurement
• Battery hydrometer for testing specific gravity
• Wire brush or battery terminal cleaner
• Adjustable wrench set
• Safety glasses and rubber gloves
• Baking soda and water solution for cleaning
• Dielectric grease for terminal protection
• Infrared thermometer (optional but helpful)

Step-by-Step Fix

1. With the motorhome plugged into shore power, measure voltage at each individual 6-volt battery and each 12-volt series pair using your multimeter. For individual batteries, measure across each 6-volt battery's terminals. For pairs, measure across the positive terminal of one battery to the negative terminal of its series partner in each 12-volt pair. You should see 13.2-13.6 volts maximum during float charging. If the problem batteries show over 14.5 volts during float charging, you've confirmed overcharging.
2. Disconnect shore power and let the batteries rest for 2 hours. Measure voltage again - all batteries should read between 12.4-12.8 volts when fully charged and rested. Use your hydrometer to test specific gravity in all cells of all batteries. Healthy cells should read 1.275-1.285, and all cells in a battery should be within 0.050 of each other.
3. Disconnect shore power and turn off the battery disconnect switch before proceeding. Inspect all battery cable connections, starting with the problem batteries. Look for white/green corrosion, loose connections, or damaged cables. Clean all terminals with the wire brush and baking soda solution, then retighten to manufacturer specifications (per manufacturer specifications (typically 75-95 inch-pounds for most golf cart batteries, but verify with battery manufacturer)).
4. Check your converter/charger settings if accessible. Many Tiffin units use Progressive Dynamics or WFCO converters with adjustable voltage settings. The bulk/absorption voltage should typically be 14.4-14.8 volts, and float voltage should be 13.2-13.6 volts for flooded batteries.
5. Replace the two problem batteries immediately. Their continued overcharging will damage your charging system and potentially cause thermal runaway. When installing new batteries, apply dielectric grease to all terminals and ensure all connections are equally tight.

When to Call a Pro

Call a qualified RV technician if your voltage measurements show the charging system is delivering over 14.5 volts to any battery, as this indicates a serious converter/charger malfunction that could damage expensive components or create a fire hazard. Also seek professional help if you find voltage differences greater than 0.3 volts between battery pairs, which suggests wiring problems in your coach's 12-volt system.

If you're uncomfortable working around batteries or lack experience with electrical troubleshooting, have a professional diagnose the charging system before replacing batteries. A good RV service center can perform load testing on your converter/charger and check the entire 12-volt system for proper operation. Given that you're on your third set of batteries in 9 years, there's likely an underlying system problem that needs professional attention to prevent future battery failures.

Consider having your Tiffin dealer inspect the charging system under warranty if any components are still covered. Document the battery problems with photos and keep records of your battery purchases, as repetitive failures often indicate manufacturer defects in the charging system that should be covered under warranty.