I have received the dreaded 601 error before my start-up process. I ran the battery check through the operating systems' diagnostics (F2) and it said it would need replaced due to use over time. I also ran the battery charge check through HP Support Assistant and it said that it was very weak and possibly needed replaced.
How do I replace my internal battery? The website that HP Support Assistant took me to only had the external batteries available.
Can we have your full model number? I think the error you are seeing refers to the "main", large battery and not the little clock or CMOS battery. Is your system closed so that the battery is not easily removeable? The full model number will point us to the right service manual which will show the part you need and the replacement process. Also need to know what country you live in.