Skip's Corner

Can AGM Batteries Suffer Thermal Runaway like Lithium Ion Batteries?

The Question –

Can AGM Batteries suffer thermal runaway like Lithium Ion Batteries: Are they safe?

The Answer –

Does everyone know that when our RG series batteries are subject to the destructive overcharge test that they do NOT thermally runaway?

They get HOT about 260F, the electrolyte boils, the water turns to steam and the excessive internal pressure opens the vent valves releasing the steam (H20) NO ACID is expelled.  This continues for about 10 minutes and as soon as the battery runs out of water the charge current stops and the battery starts to cool down to ambient.

Skip's Corner

Voltage Regulator Overcharging

The Question –

If a voltage regulator is set to 14.1 , how does it not overcharge a 12V battery on a long trip, or when the battery is back fully charged, does the regulator continue to attempt to pump 14.1 into the battery? Would that not eventually dry out the matts?

The Answer –

No, first the battery is not fully charged after an engine start or worse if the airplane has been inactive. It will take about 3.5 hours to fully charge the battery, then 14.1 IS NOT OVERCHARGING IT, merely charging it normal at RT, too low at cold temperatures and too high or overcharging it at 100F or higher, look in the O/O manual for recommended charging voltages at temperature.

If the recommended charging voltage at the battery temperature is exceeded then yes, the vent valves will allow water to be consumed and the battery will dry out, but this rarely ever happens.

Skip's Corner

Bulging Batteries

The Question –

Is a sealed battery airworthy if it is bulging?

The Answer –

Yes, this is normal when the internal gas pressure is higher than the outside atmospheric pressure, it’s a GOOD sign as each cell pressure relief valve is not leaking.

The cell pressure relief valves remain closed normally but do burp occasionally to relieve excess internal pressure while in service. The recombinant gas battery requires a positive internal pressure to operate normally.

The case will go concave if the aircraft makes a rapid descent from a high altitude.

ALL rechargeable batteries of any type are called “secondary” and ALL have pressure relief valves to prevent the battery case from rupturing or bursting due to high gas pressure that may be caused by overcharging with higher than recommended voltage from either internal or external power. Sometimes this happens to batteries that are shipped in a charged state that are of normal shape at the time of shipment and are subject to either higher or lower atmospheric pressure during transit.

See Page 9 of Document Number 5-0324 “ CONCORDE RG SERIES AIRCRAFT BATTERY OWNER/OPERATOR MANUAL “ packed with each battery.