66ST battery replacement

[NickP]

I realize that the battery pack that comes with the 66ST has a sleeve around is so that it will depress the button under the batteries so that it can be charged.
The batteries that come with the 66st seem to be failing so I'd like to replace them. I don't want to use the Garmin Battery Pack because I've never been happy with the length of time they last.
The battery pack says 2.4 volts 2000 mA. Did they arrive at 2.4 volts because each battery is 1.2 volts? That is my assumption. Also, would I be doing any harm to the GPS by trying to get higher mA rated batteries?
There a a few different techniques on how to get the button under the batteries to depress which I will try.

 

[Nuvi-Nebie]

There are some notes on the battery charging switch here :-
https://www.gps-forums.com/threads/terrible-charging-on-66st.47885/


The 66st can take 2 x AA non rechargable (1.5 Volt) batteries, 2 AA rechargable (1.2 Volt) batteries that were charged before insertion into the 66st or the same rechargeables can be charged in the 66st if the switch is activated with a piece of plastic

I have used 2500mA AA rechargeables in my GPSMAP64s which uses the same Garmin lithium battery pack