How do I modify the aircraft weight and balance after a battery replacement?
Is the Concord battery on the approved equipment list?  Is it approved to be in your airplane due to it being PMA'd?

The point is that the battery has to be approved by the FAA and if it isn't you'll need to get it approved.  It's not a major redesign requiring form 337 but a minor alteration to it's approved type certificate.

To answer your question, you can alter your weight and balance but it must be signed off by an A&amp;P mechanic.