There are a few things that can cause low power with the TM with mostly easy fixes
Easiest can be checking if the contact point of your battery door has oxidized or even gotten dirty interfering with contact. I rub mine on my denim jeans every time I change the battery. The battey terminal itself may also be dirty.
If people drop their battery in they can bend the contact on the bottom. You can pull it back out a little with a paperclip or hook of some kind. I always put my battery in horizontally to avoid this.
Even tightening the screw if it might have gotten a little loose may improve contact, though watch that you don't strip it.
One of the bigger deal power issues is a problem with contacts on the thin metal strip inside the unit. Many have added a shim under the strip at the contact point on the top of the wood with great success. I have not needed to do it but it appears to be a fairly tame self repair, especially with the great breakdown by
@JoeKickass on page 187.
I know it's a big thread, but there are lots of good suggestions in it. When you get it working up to par I guarantee you will fall in love.