There is that risk. Quality AGM batteries however can start an engine when depleted, better than a flooded battery could if depleted to the same low level of discharge.
For example two batteries one flooded and one AGM are both drawn down to 30% charged. The flooded battery might spin the engine once slowly and then the dreaded starter click occurs. The 30% charged AGM battery will likely easily start the vehicle.
My group27 northstar AGM is 90AH capacity and 930 CCA. It has started my engine with 64AH removed from it, and it was not even close to struggling.
The issue with AGM batteries is they require higher amp recharging from their most depleted state, and it is more important that they reach a true 100% recharge compared to a flooded battery.
The le$$er AGM's will list a 30% maximum charge rate, meaning no more than 30 amps per 100AH of capacity, while the higher $$ AGM have basically no upper limits on charging amps, just do not let the voltage climb above a certain level and one can feed them huge charging amps.
The high$$ AGMs are Odyssey, Lifeline, and Northstar Expect to pay ~300$ minimum for a 100Ah group 27.
Lesser $$ AGMS can be had for about 180$$ for the same capacity, but they have more limitations.
While the 30 amps is the maximum on the 100AH lesser AGMS, they still enjoy initial charge rates upto this 30 amps.
As such, they do not make great batteries when deeply cycled and low and slow solar is to be the ONLY recharging source.
But when one combines a well wired capable alternator and adequate solar, one can get excellent service from an AGM.
I used to have a group31 flooded USbattery as my dedicated house battery, and kept the AGM as the starting/emergency capacity battery.
The group31 lived out its cycle life last June, and I've not bothered replacing it, Using only the AGM for engine and house duties.
But I can plug in too and not even cycle the battery.
I am considering getting just a small Odyssey battery for emergency jumpstarting, and placing it where my large flooded battery once resided.
If one only has One battery for house and engine, then I'd recommend carrying a jumper pack such as this example:
http://www.amazon.com/Jump-N-Carry-JNC660-1700-12-Volt-Starter/dp/B000JFJLP6
I recommend not using this except for jumpstarting and promptly recharging it afterwards.
Some choose to use the small battery inside these jumper packs as a house battery, but these batteries do not have much capacity and might not be charged enough to actually jumpstart the vehicle when a jump start is required.
Most jumper packs have just a 12 or 18AH AGM battery inside:
http://www.amazon.com/D5744-Sealed-...e=UTF8&qid=1453170941&sr=1-2&keywords=UB12120
I am thinking about getting this Odyssey as my emergency jumpstarting battery as it is much more powerful than the UB12120 linked above, and can accept huge charging currents:
http://www.amazon.com/Odyssey-PC625..._UL160_SR160,160_&refRID=1AMTG8JH3HC6PM5BXXWD
But the Odyssey battery is expensive. I could get a trojan t-1275 with 150AH capacity for ~175$ so I am waffling on my capacity strategy
One thing to note is that I started out with 345 AH of total capacity, and now am at the other extreme, and down to just 90AH total, but have total confidence in my system. But part of that is my ability to plug in.