I’ve just followed these steps, and with £4.50 for a precision torx set, and £14.50 for a battery that came the next day by UPS, it’s saved me loads. The couple of things I would add are - you can use double sided tape to attached the new battery, and buy a battery with the connector already attached unless you are an electrician it saves the fuss, and make sure the connector is fully in place, it’s easy for it to be marginally out and you’ll get no power.

thanks!