I don't have a SDS200, but I do run several of my portable ham radios with a bank of parallel 4 cell LiFePo4 batteries. This produces a nice 13 V source which stays very well self regulated. Since my radios are demanding a much higher (very much higher) current draw than the SDS200 will, you won't need anywhere near the capacity I use
. My arrangement uses four 8.4 AH 4 cell batteries in parallel. Just one of these would run a scanner only radio for quite a while. The voltage on these packs need to be monitored closely, however, as over discharging them will quickly shorten their lifespan. An appropriate charger for this type of battery will need to be used. A link to the batteries I use can be found here
The charger I use can be found here.
Turnigy P403 LiPoly / LiFe AC/DC Battery Charger
It is quite convenient due to the simple single balance lead connection to the charger. It operates either from AC (US 115V, cord included) or 12 to 14V DC. My charger is 4 years old now.
Hope this helps