I don't know what's wrong with my bonsai!

[RainShine]

I'm fairly new to the bonsai care thing and I'm having some trouble. Back in June I got these two tiny bonsai tress for about $2 each (I can't remember what kind they are though) and one of them is growing very well, but the other looks like its on its way out. It was doing fine up until it started getting cold out which was when its leaves started turning brown and falling out so I moved it to a warmer part of the house, right by the back door. I water them both every couple of days when the soil looks dry but the one has lost most of the leaves and the ones still on it don't look so good either. What am I doing wrong?

Edit: They have been inside since I got them, and since I moved them they haven't been getting as much sunlight shining on them but its in the western part of the house and that doesn't get a lot of light until around 3 because the garage blocks most of the afternoon light. I've never used any fertilizers or trimmed it or anything. We have turned the heat on and the air is a lot drier now than it was in the summer.
I don't have any photos available right now but I'm pretty sure that the sick one is a snow rose bonsai

[Gnome]

RainShine,

Welcome to the forum. In order to offer any assistance we will need some more information, such as what species you are growing? As you do not know can you please post some pictures?

It was doing fine up until it started getting cold out which was when its leaves started turning brown and falling out so I moved it to a warmer part of the house, right by the back door.

I take it that the trees are inside. Is that correct? Have they been inside since you purchased them? What kind of light are they receiving? What has changed recently, central heating? Have you fertilized recently? If so with what and how much?

The more information you can provide the more relevant our responses will be.

Norm