The chassis battery may have reached end of life. Engine start batteries often appear to fail suddenly.
** THEY WERE ACTUALLY 8 YEARS OLD
Sat for 4 months at an RV park plugged into 50a power.
House batteries stay fully charged (charge off shore power using converter), but my chassis batteries are now dead (found when trying to leave) at 6.2v
If the chassis batteries were at 6.2 volts for 4 months, they are toast. If they were below 12 volts for even a month, they would probably be severely compromised.
Sulfate on discharged battery plates slowly crystalizes. The crystals are hard to re-dissolve (charge).
** YEP, NOT SURE HOW LONG THEY WERE DOWN, WASNT WATCHING THEM LIKE A DUMMY
Used Aux switch to get the rig started. Drove 5 hours and saw charge while driving at 13+ volts from alternator.
This morning back down to 6.2v
Was the RV plugged into shore power when voltage dropped? Dropping that much when not on charge means the chassis batteries are severely compromised. They are self discharging and probably not holding much charge to begin with.
** NOPE, DRY CAMPING AT END OF 5 HOUR DRIVE
If it was plugged in, battery terminal voltage should have stayed higher even with a defective battery.
In this case bridge circuit is not working properly. It could be a fuse or circuit breaker. It could be a failed relay or solid state device.
Always thought my generator or shore power was charging the chassis batteries too.
Different RV's are wired differently. Even if your RV at one time charged chassis battery from it's converter/charger, the bridge circuit may have failed. This is a common problem.
**ANY WAY TO FIGURE OUT IF THERE IS A BRIDGE CIRCUIT? TRACE WIRING OR ?
An alternative is that the chassis batteries just failed. Measuring chassis battery terminal voltage would tell. Measure without charging (static for an hour or two). You got 6.2 volts before.
Plug into shore power. Voltage should slowly rise to 13.6 or 14.4 volts. Charge for 14 to 18 hours. Unchanged voltage means bridge circuit is not working.
For safety, monitor the battery temperature. Some battery failure modes can cause high temperatures while charging. Just use your hand to test temperature. Uncomfortable temperature mean batteries are bad.
Voltage on good batteries will slowly drop to 12.7 volts. A self discharging battery will continue to slowly drop, possibly to 6 volts.
** GREAT INFO - I AM WATCHING NEW BATTERIES & WILL CHECK THESE OUT OVER NEXT FEW DAYS
Going to replace them today but concerned I have some weird phantom draw that has just shown up.
Any thoughts on wiring to make sure the converter charges chassis batteries at same time as house batteries? Concerns?
Install new chassis battery. Make sure new chassis battery is charged. Voltage should be above 12.4 volts. They may test at 12.7 volts if they come fully charged.
** NEW BATTERIES WERE AT 12.7v & 12.8v at purchase
If new battery voltage is above 13.2 volts, wait a while. After 1 to 4 hours the voltage should drop to less than 13.0 volts, possibly down to 12.7 volts.
** INSTALLED 2 NEW BATTERIES TODAY. I NEGLECTED TO SAY I HAVE A SMARTBMV I INSTALLED LAST YEAR TO WATCH MY NEW HOUSE BATTERIES AND I DID INSTALL THE AUX LINE TO MY CHASSIS BATTERY, JUST WASNT WATCHING THEM
Plug into shore power or run generator. Voltage should slowly rise to 13.6 volts or 14.4 volts. If voltage does not rise, bridge circuit is not working. If it does no reach 13.6 volts. Bridge circuit is not working properly.
** OK WILL LET THEM REST FOR ABOUT 6 HOURS THEN RUN MY GEN & SEE WHETHER IT TRIES TO CHARGE OR NOT
It may take a while to start rising. Some bridge circuits would not start charging the chassis battery until house batteries are above a certain voltage. Some just have a built in delay. Some bridge circuits have different programmed behavior.
** UNDERSTOOD. I WILL RUN FOR 4 HOURS TO TOP IFF HOUSE BATTERIES & SEE IF CHASSIS BATTS START CHARGING OR NOT
House batts only a year old & doing fine. Chassis batts at least 6 years old - there when I bought the rig, but were always strong
6 years is a long time for a daily drive vehicle. The RV situation depends on how often the vehicle has been started and run.
** WE SIT FOR ABOUT 4 - 5 MONTHS A YEAR IN A RESORT WITH 50amp POWER. I JUST WASNT SCRUTINIZING MY CHASSIS BATTS - WE LIVE IN IT FULL TIME SO NOT IN STORAGE. JUST A GOOF ON MY PART I THINK
It also depends on how low the terminal voltage got during storage. 12.4 volts is the minimum for long term storage. It is the same for house batteries.
I wish you good luck and happy trails ahead!