Yes, it will take roughly twice the time, however you should monitor the charger itself for overheating, charger topologies are varied to say the least, if the charger was just barely able to charge the #1 battery safely then the extra time it takes to charge the #3 battery might be more than the charger can handle in the long run. Just keep an eye on it, I tend to err on the side of caution, even if unwarranted simply because you can't be too safe, you can however be not safe enough =)