#2 batteries

Have you ever changed your own #2 batteries? They are expired after two years.

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Others who know more than me may chime in. Not many people monitor the guest section and most people will say join COPA and you will get advice and information far more valuable than the $95 annual membership/subscription fee.

BAT 2 is supposed to be changed every 2 years, but a recent service bulletin indicated there are some bad batteries out there, they may not last that long. However in some cooler climates where the plane is flown regularly and therefore kept charged frequently (ALT2 charges it), it may last longer.

You may change them on condition, rather than on the periodic basis, if the plane is not used for hire (NO commercial activity), but I personally change mine at the two year intervals. Battery changes are owner maintenance if you can read the maintenance manual, have the tools, the patience, and don’t mind being squeezed into a small space in the tail of the aircraft while you do it.

It’s kind of a hateful job, many people let their friendly neighborhood A&P suffer, er I mean keep food on their table and have them do it.


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Yes, not fun, but doable. I have done it a couple of times. Protect your ribs at the access hole edges! Have good lighting, a mirror and tools to find the back side hardware that falls out of sight.

Thanks for the replies.

I did it on my G1 Cirrus, once. As mentioned, it’s a PITA to do. Also, you have to be careful which battery you buy. You have to get the ones with 1/4" terminals (which is not the default). You will see these designated as “F2” terminals. Do not get batteries that have F1 terminals with adapters. They will not work at all in G1’s as they don’t fit. DAMHIK. Some sellers do not know the difference and will ship you an F1 battery with adapters after swearing that they sell an F2 battery.

Does bat 2 power Caps……or does it have its own battery?

Yes, CAPS receives power from both BAT 1 (via the constant power bus), and directly from Bat 2.

No, the CAPS system does not have its own battery.


I’ve gone 7 years with battery 2. I thought they would be bad by now, but they still are passing a load test. I only turn on battery 2 for a minute to verify the flap light is off. Then I turn on battery 1 and start the engine. The batteries get charged weekly (for an hour or two) when I fly. So my guess is battery 2 never gets run down. The lack of constant charging probably helps also.

These SLA (sealed lead acid) batteries are used in security systems. They typically last 5 years. They are trickle charged continuously. Plus they get drained when an electrical storm takes out the power.

This year, I will replace the battery 2 during the annual. I’m starting feel nervous about it… :slight_smile:


Do you have an industry accepted load test for the #2 batteries Paul?


Yes, the avionics that are turned on with battery 2. Battery 1 is off. Time 30 minutes and read the voltage. If it is over 21 volts, it passes.

I’m sure you know, but for newbies it is imperative to immediately recharge the battery after any cap check. Storing lead-acid batteries in a partially-discharged state will hasten their demise.

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You are right. Pretty much kills them.

Also do a slow trickle charge to bring them back up. No fast charging.

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