My personal experience is that I have had the Aico 10 year battery powered alarms in my home for 8 years now and there's no suggestion of the battery failing in any of the units. I installed the same ones in my daughter's flat 6 years ago, no problem so far. I have installed quite a few over the last 3 years, so maybe too early to tell, but I have no doubt the technology will see these battery units last 10 years.
FYI, my system and the system in my daughter's flat were installed as both properties were rented out. This was before:
1. The recent regs for ALL homes to have them, and
2. The recent regs allowing for battery radio-interlinked units.
My approach previously was a hybrid one, whereby the first unit was a mains powered unit with 10 year battery and radio-link, and the others were purely battery powered radio-linked. While not strictly complying when fitted, the design and construction of the properties was such that hard-wiring would be very messy, very time-consuming, very expensive. Also, both properties had the usual smoke in the hall, heat in the kitchen and smoke in the main living area. These 3 detectors are less than 6m apart, so if one sounds you really hear it throughout, whether they are interlinked or not!
Nowadays, they comply anyway so not a problem, and I live in the previously rented property and my daughter lives in hers.
I just think that the simplicity of the non-disruptive 10 year battery radio-interlinked Aico alarms is a great system, and my clients over the last few years have been very happy too chose that option.