My Datatool 3 has played silly buggers a few times. I replaced the battery - and yes I know yours is only a couple of months old but the silver oxide batteries have a limited shelf life.
Can't remember the code for them, but it might be worth either getting a pair of batteries fmor a watch repair shop (or camera shop - should be under £5 each) or try the other remote. Don't be temped to get batteries from the local market though, they are likely to be old stock.
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