Hi I have a Toyota Alphard 3.0 VVTI Petrol 2003 which i have owned for only 2 months now and gradually finding various issues to fix

My problem is : The existing battery is going flat quickly on a regular basis and i dont know how old the fitted battery is? and dont know how to check the condition any suggestions?.       I am currently trying to charge it but if succesful unsure how long it will hold the charge for?

it is a Numax Premium 005L 12V 60AH 510A (Size: L230mm. W170mm, H225mm) (battery tray is not much bigger)

Can anyone please recommend what they would replace this battery with? i.e. has it got to be an 005L code battery or is there a better one with different code?                                        I have looked at the Tanya batterys website which appears to be a wide choice is excellent and great value, However I am thinking of buying a Bosch S4 024 005L 12V 60Ah 540A battery £68 from Costco as it comes with a longer 5 year guarantee and with Costco you can return it anytime if there is a problem for a replacement.                                                     What are your thoughts and opinions?

We bought a higher rated Tanya battery with the same terminal layout and that stopped our dead battery issues. I have to modify the tray slightly on one side but fits perfectly now.