Ryobi 36v charger (Acacia Gardens)

As a newbie to the world of rechargeable tools I purchased a Ryobi in the 36v range for my hubby. As it was a garden tool that would be rarely used the battery became so flat that the charger can’t recognise it to recharge it. We’ve since moved on to the 18+ range. You’re welcome to the battery if you know how to get charge without blowing yourself up 🤣🤣🤣