pinpointer batteries

I have had my whites pro pointer bullseye trx for about 5 years and until last weekend, it was working pretty good.
Then it started beeping slowly when not near a target and with all the detectors turned off and any metal we had wasn`t near it ,but beeped fast ( as it should )
when tested on something like my pick. Put the pinpointer in the hole i am digging and it has a slow beep and speeds up if something is there ,but take it away from that target and put it back where the target was and i get nothing. Lift it out of the hole and it sometimes get a slow beep .
Turn it off and on again and it temporarily seems to fix it ,but not for long.
Just weird.
I worked out the batteries haven`t been changed in about 18 months` ,so i put in 2 fully charged re-chargeable AA`s ( coles brand 2200mah 1.2v ) before i went out this morning,but it seems to be doing the same thing. Turn it off and on again and it temporarily seems to fix it ,but not for long.
I am still finding or locating stuff with it ,but it is inconsistent and i am not as trusting of it as i used to be.

Can dodgy batteries or re-chargeable batteries make the pinpointer play up ? The re-chargeable batteries i used today were charged for 6 hours or so. Is this really enough time for them to be strong enough for the pinpointer ?

I don`t wear a watch or rings and the keys on my pocket were well away from the pinpointer.

I`ll put my finds up once they are cleaned. We got washed out today and had to leave.

Thanks
FOZ

Rechargeable batteries may not have the have same voltage as ordinary or lithium batteries. If I remember rechargeable are 1.25v and others 1.5v double them up and the difference is 2.5 versus 3 volts. Just a thought.