Other failure modes in flooded cells are related to grid corrosion and acid stratification which are not discussed in the present paper. The increasing demand from lead-acid batteries to operate in deeper depth-of-discharge namely 20-30% DOD, emphasizes further the above described problem of sulfation. Due to sulfation, SLI batteries are planned to work at a shallow DOD. Their cycle life becomes very limited when they are forced to operate at 20-30% DOD. In order to solve the sulfation problem in deep cycling of SLI batteries, carbon materials were added into the active-masses of their electrodes . It is universally accepted that carbon materials as additives enhance the performance of these batteries in terms of higher charge-acceptance, which is the key metric for addressing the sulfation problem. However, controversy arises regarding the preference of carbon allotrops, which renders the best perfor- mance. Graphitic powder, carbon black, various activated carbons are already introduced by several industries and their use as ad- ditives indeed enhances performance. Apart from that, carbon- based nano materials like single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT) and graphe- nes are envisaged as most efficient materials, because of their or- dered structures and consequently high intrinsic electrical conductivity. However, exploring the use of carbon-based nano- materials in lead-acid batteries was very limited so far. In any event, it is clear that extending battery life cycling at both low and high DOD values definitely remains one of the most important challenges for this battery technology.