Bosch is an good battery brand and it being under the seat will certainly offer some protection from cold and heat but, that said, I would still say to change a battery (even a seemingly healthy one) at max 7 years. A dying battery can burn out a perfectly good alternator in some cases by overworking it (although, this tends to be if you do a lot of stop-start driving/short journeys). Batteries degrade over time and if you've avoided typical things that catalyse the battery draining then that would partially explain why it's lasted so long. These include lots of short trips, fluctuating temperatures, lack of use etc). Even so, I'd get it changed sooner than later. Your car may be running fine, but it's all the electricals that you need to keep an eye on. For example, are the instrument panel lights markedly dimmer than the day you bought the car?