TomTom Watch

I bought a TomTom watch from your shop in Dec and I was given a used watch and I subsequently returned it. I was given another watch, which does not seem to have a battery life that lasts more than 2:30hrs or lasts up to anything more than 24kms, now that I am doing longer training, this has become a disappointment. I enquired with TomTom and they have confirmed that battery life for this watch is 6-7 hours and also that in Dec, I should not have been sent this type of watch. I have changed the settings on the watch to what TomTom said I must do and the batter still would not last. I bought the watch together with a friend and her watch lasts over 5:30 hours and remains still with battery life, I charge the watch over night to make sure it is full and it doe snot matter how long I charge it, it will not last over 21kms which I do in 2hrs. Kindly help as I think that I have been sold a lie and that for the amount of money I paid for this, this is totally unfair. Thank you