Hey, @steve5964.
You could try replacing the battery, as it is much cheaper than an $800 motherboard. iFixit sells batteries for your exact model [product|IF245-494|here|new_window=true], and they're significantly cheaper than a motherboard replacement. It should only take about fifteen minutes, but you must do it with your own knowledge, as iFixit doesn't offer guides for this model. I hope this helped you solve your problem today.