Bought a 100ah lithium battery (https://www.amazon.com/gp/product/B084DB36KW/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1) for my camper van build, but it's been sitting around for 3 weeks now since it was delivered. I just realized I am supposed to always keep it charged? How can I do this at home when the camper van's electrical system is not yet complete? I googled searched quickly and am not understanding what I need to do. Can someone dumb it down for me and tell me exactly what I need to do to keep this battery charged until I can finished the van's electrical system and install it? Hopefully something that does not involve buying any more special equipment! I have a trickle charger but apparently that's not good enough.