A simpler method of protecting the ammeter would be to put a shunt across the terminals to bypass some of the current flow while still allowing it to indicate charge/discharge conditions. I like to use a piece of stainless steel radiator hose clamp bent into a horseshoe shape on the ammeter terminals to carry most of the current. It has just enough resistance to shunt enough of the current through the meter to make the needle deflect.+/-.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!