What TYPE of batteries should I buy for my new GPS?

I have bought a new GPS machine. I’m debating on the type (rechargeable or disposable) batteries I should buy for this machine.
%I can buy rechargeable batts. (@ $8.00 a-piece +$15.00 for the recharging dock)
or disposable batts (@ $6.00 a-piece) every time I use this unit.

I have already used up the first set of disposable batts after only two uses of my GPS.
I’m seeking suggestions and advice.
Thanks.

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